The present invention refers to a method and a system for controlling the movement of a mast of a drilling machine, in particular for obtaining piles.
Foundation drillings and consolidation of the ground are generally accomplished using drilling machines of the self-propelled type, having a framework on wheels or support tracks, a rotary turret on a fifth wheel provided with a power unit (heat engine or electric motor), cabin, control accessories and typically winches for lifting the drilling accessories. The machine comprises a mast provided with sliding guides on which the rotary table (also referred to as “rotary” in the industry) linearly translates. The rotary receives power, for example hydraulic or electric, from the power unit and converts it into a rotary motion adapted to move the drilling tools. The mast is delimited at the upper part by a head comprising pulleys for returning the ropes, through which the winches arranged on the turret or also on the mast itself, lift or lower the bank of bars or the drilling tools. The latter are generally unconstrained in the axial direction, but not in the radial direction, from the rotary table which has an autonomous lifting/lowering system.
In the cases that require extremely deep drillings the technical solution typically used is that one of applying the drilling means in a bank of telescopic bars (also referred to as “Kelly bars” in the industry). Such bank of bars is generally constituted by several elements with decreasing section axially slidable one within the other and capable of transmitting rotary motion and the thrust force required for the advancement.
The banks of telescopic bars are generally divided into two types, friction bars and mechanical lock bars.
In the friction bars, the torque between the bars is usually transmitted by means of longitudinal strips welded along the elements the bar is made of, both internally and externally, so that they are engaged to each other. The transmission of axial thrust between the bars occurs by means of friction between the strips of the bars which is generated in the presence of torque. Likewise, the external element of the bank receives the rotary motion from the rotary table through the engagement between the strips of the rotary tube and the external strips of the bar, while the axial thrust transmission occurs through friction between the strips of the rotary tube and those of the external bar which is generated in the presence of applied torque. In the absence of applied torque, the bars are axially slidable with respect to each other and the entire bank is slidable with respect to the rotary table, moved by a suitable flexible means, preferably through a cable.
In the case of the mechanical lock bars, on the external bar, at the top, at the base and sometimes also at the intermediate position there are generally obtained some seats where there are engaged the strips of the rotary tube remaining axially locked. This allows transmitting both the torque and the thrust through an abutment with a mechanical stop on the strips and not only by friction. When the strips of the tube are engaged in the seats of the external bar, it is axially constrained to the rotary. Rotating in the opposite direction of the rotary allows disengaging the strips of the tube from the seats of the bar thus making the bar slidable with respect to the rotary. The same system is used for the transmission of torque and thrust between the bars: at the bottom of each bar there is obtained a tube with strips facing inwards, which end up engaged in the seats of the innermost bar.
During the drilling, all the internal elements initially slip from the telescopic bar and progressively with the depth of the drilled hole, the internal elements continue the descent. When the most external one of the internal elements reaches its lowest position it settles in mechanical abutment on the most external element which is on the rotary. The remainder of the internal elements then further continue the descent until the next most external one of the internal elements reaches the lowest position and settles into mechanical abutment with the previous most external one of the internal elements. This continues until the last of the internal elements is in its lowest position.
At the end of the drilling step, extracting the tool from the ground requires returning the bank of bars to the minimum length retracted configuration. This occurs by actuating the winch, generally referred to as main winch, usually mounted on the base machine (on the turret) whose rope—after being returned to the head of the mast—ends up connected to the upper end of the innermost element of the telescopic elements that the kelly bar is made of. The winding of the rope on the drum causes the re-ascent of the most internal bar which at the end of the travel thereof progressively draws the intermediate bars and then the more external ones progressively.
Frequently, on the base machine (turret) and sometimes also alternatively on the mast, there is installed a second winch, called auxiliary or secondary winch, whose rope is returned on the head and has—at the free end—a hook or grip members which allow lifting the loads, armatures or required equipment which should be moved during the operating steps of execution of work. In this type of machine, the sliding of the bank of bars is made autonomous with respect to the sliding of the rotary table on the guides of the mast. In addition a dedicated system, such as a hydraulic cylinder (for example, a preferably long stroke cylinder or a multi-acting hydraulic cylinder) or a third winch (referred to as “pull-down” winch in the industry) is installed to allow the sliding of the rotary table over the entire length of the mast itself (in the case of the winch) or in the first lower half thereof (in the case of the cylinder). Usually, the third winch, when present, is mounted almost exclusively on the mast and not already on the turret of the machine and it is returned on the ends of the mast to exert pulling and thrust forces on the rotary.
In order to reduce the front and lateral oscillations and diversions of the bank of telescopic bars with respect to the mast during the drilling, there may be present a bar guide head slidable on the mast and connected to the upper end of the external bar. Such connection allows the rotation of the bank but prevents the relative axial sliding between the bank and bar guide head which is thus drawn by the bank bars when the latter slides with respect to the mast. It performs a function of limiting the radial oscillations of the end of the kelly bar, especially when executing inclined or not perfectly vertical drilling.
In order to prepare the machine for transportation on the road network outside the worksite it is necessary to recline the mast up to bringing it to the lying or horizontal position so that the total height of the machine in transportation configuration is the lowest possible and allows meeting the height limits requirements set by the road requirements. The mast may be laid at the rear part on the turret or at the front part, cantilevered on the font part, at the front of the cabin. Any components exceeding the allowed maximum height must be disassembled for transportation and thus reassembled upon reaching the worksite.